Recently, Swedish and American neuroscientists have successfully used brain transplants to treat neurological and neuroendocrine diseases in rats and to a limited extent in humans. Thus we intend to study the effects of the fetal hypothalamic transplants on the neuroendocrine control of reproductive senescence. The hypothalamus from a 17-18 day old fetus will be transplanted into the anterior third ventricle or preoptic area of hypothalamus of an old rat brain. Both old male and female rats will be tested. Changes in gonadal function will be followed by gross and histological examination of reproductive organs and reproductive tracts, and by measuring sex steroids, LH, FSH and prolactin. Estrous cycles will be monitored by taking daily vaginal smears in females. The activities of catecholamines and LHRH in select areas of hypothalamus will be determined by high performance liquid chromatography (HPLC) and by radio-immunoassay (RIA). Attempts will be made to restore estrous cycles and to induce normal pregnancies and parturations in old female rats that have ceased to cycle, and to increase serum testosterone levels, sexual activities and fertility in old male rats, by the use of fetal hypothalamic transplants to rejuvenate hypothalamic function. Attempts also will be made to prevent the decline of neuroendocrine function by hypothalamic transplants, which in turn, may improve the quality of late life and extend the life-expectancy.